Austria-Hungary was not a particularly useful ally from Germany's point of view.
Central power
That would be Germany.
Germany was the biggest central power in WW1 but the Otoman Empiere also was in it with Austria Hungary.
Austia-Hungary did not exist anymore in WW2. It became Austria and Hungary, two separate nations. Austria was annexed to Germany in March of 1938. Hungary became a German ally.
It was Germany,Bulgaria,and Austria-Hungary.
Germany, austria-Hungary, Bulgaria, and the ottoman empire
they were only defending their ally, Austria Hungary, which was attacked by Serbia
Yes. Russia entered a regional conflict between Austria-Hungary and Serbia to protect its fellow Slavic nation.
It didn't. Austria-Hungary was a huge powerful empire. Serbia was weak and tiny. The one advantage Serbia had was its ally, Russia, but Austria-Hungary had Germany to back it up, which nullified that possible advantage.
Austria-Hungary is on the continent of Europe.
Germany, Italy, and Austria-Hungary signed a treaty to help each other if any of them got into a war. Britain, France, and Russia had a simular agreement to defend eachother from Germany, Italy, and Austria-Hungary. That basically divided Europe into 2 teams. So when Austria-Hungary attacked Serbia who was an ally of Russia everyone was dragged into the war.